The invention relates to an apparatus for producing an electrical signal having a voltage value which varies with an angle of rotation, and more particularly, to a potentiometer having a pair of semiconductor magnetic resistance effect elements which cooperate with a permanent magnet mounted on a rotatable shaft.
The conversion of a rotary motion into a translational motion by way of a potentiometer interposed between the both motional systems to derive an electrical output which varies as a function of a change in the rotational motion system and which is utilized to control an electrical drive to the translational motion system is extensively employed in many industrial fields, for example, numerically controlled machine tools, automobiles, electronically controlled sewing machines and the like. A potentiometer of this kind is fully described, for example, in U.S. Pat. No. 3,745,503 which is assigned to the same assignee as the present invention. A potentiometer of the prior art provides an output which is a linear function of the angle of rotation. Specifically, a semi-circular magnetic field is established for angular movement together with a rotary shaft about the axis of the latter, thus scanning a pair of magnetic resistance effect semiconductor elements each having an arcuate sensor surface and disposed annularly about the axis. The annular sensor surfaces of the pair of elements form together a circular band of a uniform width, so that a change in the area of the sensor surfaces of the elements exposed to the magnetic field varies in proportion to the variation in the angle of rotation, thereby causing a proportional change in the resistance of the elements. The pair of elements are connected in series across a d.c. source, and hence the potential at the junction between the elements also varies in a proportional manner.
Generally, it is considered desirable to have a linear function output from a potentiometer to produce a proportional translational motion in response to a rotary motion. When such a potentiometer is used, distortions in the conversion response may be caused by mechanical errors of the translational motion system and tracking lag and often must be compensated for by the use of a potentiometer which produces a non-linear function output. On the other hand, a potentiometer having a predetermined non-linear function output is demanded recently in complicated machines utilizing an electronic control in order to achieve a non-linear relationship between the rotary motion and the translational motion. The prior art failed to meet such requirement.